Radar indicator sweep deflection system



May 8, 1956 Q SYMER, JR 2,745,036

RADAR INDICATOR SWEEP DEFLECTION SYSTEM Filed Oct. 21, 1954 2 Sheets-Sheet 2 Ampllfude o )y V q- Amplitude iRADAR INDICAToRsWEEP DEFLEcTroN f SYSTEM Orten H. kSyrneiyvJr., Wantagh, N. Y., assignor to Hazeltine Research, Inc., Chicago, lll., a corporation of lllm Iois Application october 21, 1954, serial No. 463,650 .v sciaims. (ci. 315-22) This invention relates to radar indicator sweep deflectionsystems and, particularly, to such systems of the type producing closed-center plan-position radar displays.

Radar indicator sweep deection systems heretofore proposed for producing closed-center plan-position displays also inherently produce a certain amount of undesirable distortion in the portion ofthe display adjacent the center of the display screen. This distortion is primarily caused by undesirable distortion in the initial portions of the sweep signals which control the electron scanning beam of the display device. Previous efforts to reduce this distortion have been in the direction of utilizing more expensive sweep-signal generatorA circuits, sweep-signal amplifier circuits, and deection circuits. Such efforts have not resulted in complete elimination of the distortion and have led to the utilization of more complex and expensive circuitry than is desirable for many applications.

It is an object of the invention, therefore, to provide a new and improved radar indicator sweep dellection` system which avoids the foregoing limitations of systems of this type heretofore proposed. y

It is another object of the invention to provide a new and improved radar indicator sweep deflection system for eliminating .display distortion normally occuring adjacent the center of the display.

f It is a further object of the invention to provide a new and improved radar indicator sweep deflection system of relatively inexpensive construction for eliminating display distortion.

Reference is made to copending application Serial No` In accordance with the invention, a radar indicator sweep deflection system comprises a display device including a display screen and means for scanning the display screen with a beam which is periodically unblanked to develop on the display screen the display of target echoes of periodic radar signals. The sweep deection system also includes circuit means for generating periodic sweep signals inherently having undesirable characteristics during the initial portions thereof and individually starting a predetermined interval prior to the corresponding radar signal to control the scanning beam. The sweep deflection system further includes meansy for supplying olfcentering signals to the display device to enable the scanning beam to start from an off-center position for each scan and pass across the center of the display screen at the end of the predetermined interval.`

The sweep deection system additionally includes circuit means for unblanking the display device as the scanning beam crosses over the center of the display screen For a better understanding of the present invention,

ice

together with other and further objects thereof, reference is had to the following description taken in connection with the accompanying drawings, and its scope will be pointed out in the appended claims.

Referring to the drawings:

Fig. 1 is a circuit diagram, partly schematic, of a complete radar system including a radar indicator sweep deflection system constructed in accordance with the present invention; Y

Fig. 2vis a graph representing signals developed at.'

various points of the Fig. l sweep deliection system and used in explaining the operation thereof;

Fig. 3 is a plan view of the display screen of a display device used in the sweep deflection system of Fig. 1, and Fig. 4 is another graph representing signals developed at various points of the Fig. l sweep deflection system.

Description and operation of Fig. 1 radar system high-potential control pulses which are, in turn, suppliedl to the transmitter 12. In response to the high-potential pulses from the modulator 11, the transmitter 12 generates bursts or pulses of radio-frequency energy which are supplied through the duplexer 13 to the antenna sysy tem 14, 15. y

Also coupled to the duplexer 13 and antenna system 14, 15 is a receiver 16 which is effective to derive and.

amplify the video-frequency components of the radiofrequency radar reply signals intercepted by the antenna n system 14, 15. The duplexer 13 enables the antenna system 14, 15 to be used as the receiving antenna while protecting the receiver 16 from the high-power bursts ot' energy from the transmitter 12. The video-frequency components from the receiver 16 are suppliedto a radar indicator sweep deection system 20 constructed in accordance with the present invention as will be morefully explained hereinafter. The synchronizing circuits 10 are also coupled to the sweep dellection system 20 for sup-v plying suitable timing pulses thereto.

The units 10-16, inclusive, may be of conventional construction and operation so that a detailed description and explanation of the operation thereof are unnecessary herein.

Descrpton of sweep deflection syslem of F ig. 1

Referring again to Fig. 1 of the drawings, there is represented a radar indicator sweep dellection system 20, constructed in accordance with the present invention, comprising a display device 22 including a display screen 23 and a scanning beam for scanning the display screen which is periodically unblanked to develop on the display screen 23 the display of target echoes of periodic radar signals. The display device 22 may also include first and second deflection windings 24 and 25 for enabling the scanning beam to radially scan the display screen 23 to develop a plan-position display ofthe target echoes thereon. For some types'of display devices, for example, those utilizing a rotating deection yoke, only a single decction winding may be required.

The sweep deection system 20 also includes circuit means for generating periodic sweep signals inherently having undesirable characteristics' during the initial portions thereof and individually starting a predetermined interval `prior to the corresponding radar signal toA concircuit means may include, for example, first and second s Patented May 8, '1956 The synchronizing Y' sweep'-signal generatorsfB-and 29, of ,conventional construction,n for `generating. lirst-andasecond-setsy of--peric-dicy sweep signals. Thiscircuit means may further include circuit means for individually starting the sweep signal's a predeterminedinterval-'prior to A4'the corresponding --radar Vsignals comprising, f'for example, 'a' sweep gate' generator l130, of conventional construction, y'cou-I pled to the synchronizingicircu-its and-tira"cla'nip-A ing circuit 32, of conventional construction, :associated with the-north-sou'th (NLS) sweep generator 2'8'an`dfa clampi-ngcircuit '33, of conventional construction, associate'dlwithf the east-west (E-W) sWeep--generator -29.

The sweep deliection system 2() preferably also' incluldes circuif-means for'varying'the'arnplitudes of fthe sweep signalsl in af sinusoidal -manner, -the sinusoidal-variation -of the first set of sweep signals ldilering-` in phas'effro'm ,the sinusoidal variation ofthe'second set 'by 90 `to enable succcssiveradial;beam scans Yto-progre'ss around the l'display.- screen 23 inacircularmanner. -This circuit means mayJ-include, for example-asine-cosine signal generator V35 for I supplying a sine-wavesignalto theyflrstrsweepsignal generator, v for example, the N-S sweep generator 28, and for supplying a cosine-wave signalto thesecond sweep-signal generator, for example, the lE-'W ysweep generator 29, 'for vvarying ,the `amplitudes of the l,sweep signals 'developed/,by the sweep,generator2 81in accordance with the sine-wave signal 4,and for Varying thefamplitudes vof ,the ,sweep signals developed .bythe E-W sweep generator 29 Ain accordance withthe ,cosinevwave signal.

ably connected as indicated` bythe dasl1e,d, line,36 to `the rotatable antenna system,14,.15, rotation of oneof the windings of the direct-current resolver in accordance withrotationof Vthe antennasystem.14,'f15 ,serving l-to produce in. apair ofstator windings of theresolverthe desired sine-.wave and Ycosine-Wave signals.

The sweep deflection system additionally lincludes The lsine-cosinesignal lgleratormayy include, for example, a conventional direct-,current resolver ,suitmeans for supplying off-,centering .signals to ,the @display device v22 Vto enable the scanning -beam to .start Vfrom anolfcenterposition for cach-.scan yand pass,.across the center ,of the display .screen 23 -at theend of the mentioned predetermined interlval. comprise, for example, circuit means for .supplying sinusoidal offfcentering signals of inverse ,phaseto the K sinusoidal ,amplitude variations of the .sets of sweep signals developed vby the `sweep generatorsv 28 tand. 29. More specifically, thiscircuit means may,inclu de, forex amp1e,..lirst and second ,phaseyinverter. circuitsand 15g-of .conventional construction, coupled ,tothe sinecosine, signakgenerator, for respectivelydeyeloping inverse phase sine-wave and cosine-wave ol-,centeringsig- This.circuitfmeans.may` Y p and the inverse-phase sinewave signaliand supplying theteombinedmsignals `-tov thelrst fdcectienwwinding `144 ofthe display device 22. The resistors 44 and 45 are connected to an input resistor 46 of a sweep amplifier 47 which, in turnis'coupled to the deflection winding 24.

The sweepv deflection system 20 likewise may include, for example, a second adding circuit S0 which includes an adding '.-resistor` 51 .-;coupled tto'fthc wondtswnepigenerator 29 and an adding resistorr52 connected to the second lphase-inverter circuit 39 for` adding the second set of sweep signals ydevelc'ipedl-byithe' generator andsth'e f inverse-phase cosine'wave signals developed b'y'theph'e inverter 39 and supplying the combined signals tothe second deflection winding' 25 of '.thenldiqzhyezdcvi; 22. The adding resistors 51 and`52 are Yconnected, for example, to an input resistor `53 o"f a' sweep amplier 54 which, in turn, is coupled to the deliection winding 25.

The sweep dellection `system 20 further includes, circuit means for unblanliing the display Adevice -'as"the scanning beam crosses over Athe center rofhe display screen-to enablethe device/ 224 to ldisplayfthesubscqucnt` l v portion-'of -each scan Whichfis -controlledibyI thelaterjportions of thesweep s ign'als. "This-unblankin'gicircuitmcans 1 may include, for example, anunblankingj-gategenerawr 56 coupledto` the display device l22 for supplying periodic unblanking gate signals thereto. 'The ^unblanking -gateV generator p56 is Ialsoy coupled to *the* synchronizingcircuits 10 fonreceivingsuitable Atiming *pulses* therefrom. VThough not-shown'inFig. 1,-itjshoul'fl' b 'emotcdrthat a sweep deflection systemin accordance withtliefpres'elrt*A invention is readily yadaptable'toinclude@provisi`onf0r71:he` frequently `desirable 'feature of -adjustable off-t:ent'e'1`ir'1gV ofthe entire Aradar scene displayed on Y the display-screen 23. Additionally, the system is -readilyjadaptableqper#' mit display of yadditional information 'on I'the display screen 23 by utilizing time-sharing techniques. -In fthis mannenfor example, anjelectronic cursor might -be made torappear on ythe display screen "23. To nutilize either -of these features, the `proper circuitry-could' wbeco'nnecjtetL for example, throughadditional gaddingj'resistors'ftothc input circuits ofthe sweep amplitiers47 and't54.

' Operation of'sweep'dflectio system'dflFigfI #Consideringnow `'the operation 4of 'the sweep'fdetlection systemjjust described,v timing fpulsesy fromY'theynchronizing :circuits 1'0 are effective f tol cause fthe transmitter'l'l2 to transmit periodic radar signals representedhby the nals. The amplitude of the signals supplied to the phase i inverters 4'38, W39 `'may i be suitably Eadjusted Aby means of voltage` dividers .40, .41, respectively, coupled .to-,the inputgcircuits of the: phase., inverters.

,Developinggthe olf-centering signals-,by utilizingZplhase inverters A38 .and 39 is intended yfas ta `representative .Y exampley onlyfas `several suitableA alternatives arefeadily.I apparent. .-.For example, `.some ,types of :sweep generators .y

giye .the desired.r phase inversion .to the sinusoidal .signal appliedthereto, .thatis, the-.sinusoidal amplitude modulatien: of, ,thesweep signals developed? byf-suchp :generator isfreinversephase to .themodulating .sinusoidal signal inverter, cireuit foraddingtherst. set. otsweepsignals t4-t5, to enable;tlie scanningl-be'am'of thedevicertofpresupplied `to lthe I unblanking gate generator which winl response thereto develops :periodic -funblanking :gate

signals represented by curve B of 'Fig'.v'2foccurringf,ufor exampleyduringithe intervalsftift's andft'ita. "'R'Fhes'e unblanking gatesi'gnals are fsupp'liedto, fork :example-1a' control electrode -off` thc'display.- device22 'forgperiodically unblanking the display device, --su'ch as duringS-intc'ryal sentv a visibleA trace onfthefdisplay .screen23p "Inconventional radar systemsemploying -planposition indicators, fthe scanning beam is periodically' 'caused :to scan the display screen '23"in -a radial-=manner,1that is, each" scan 1 starts at the center v-of the Idisplay `screen and y'sweeps `out lradia'llytol the edge-oftthefdisplaywscreeri as l"shown in 'more "detail"- i111 the enlarged cview fithesidisplay` screen f2.3 of fFig'." 3. PSuccess'ive radiali-beam sscans, as indicated'by-.thel solidilinef-traceslfl), v61, Landini, are caused to progress around fthe `center Aof .the Lfdisplay yscreen'inra/circular Vrnannera's shown. `=Each radiallsc'm' starts from the center `of'the display screeniat-fthetime of occurrence of fone -of fthe' vtransmitted -radar pulseserepresented byy curve A-of`Fig. 2v andreaches'gtheedgefof the display screen at a 'ti'rnevcorresponding 't0"'lhe"timc`jre' quired "for a target'echo to be received from aftarget at a distanceL frornthe radar antenna Y14, `15' correspondfing', to the maximum range under observation. In thisv manner, as thev directional radar antenna rotates, succes'sve beam scans progress or rotate around the center `offthe display screen inr avcorresponding manner soA that theresulting display represents a map of the surrounding terrain.

As mentioned, in rsystems heretofore proposed, the display on the display screen 23 has suffered from dis` center of the-display and out to the edge of the display screen, and unblanking the display device as the scanning beam crosses overthe center of the display to enable only the subsequent portion of each scan which is controlled by the later distortion-free portion of the sweep signals tobe visible on the display screen 23.l The start of each beam scan from an olf-center position is 'indicated for the representative scans 60, 61, and 62 of Fig-3 by the' corresponding dashed line traces 60', 61', and62'. As the display device is blanked during the portion of the traces represented by the dashed line segments, this portion of each beam scan does not appear as a visibleV indication on the display screen. It is during this invisible portion of each scan that the dstored part of each sweep signal occurs so that as a result no dis? tortion is observed in the visible display pattern.

To this end, the sweep gate generator 30, in response to timing pulses from the synchronizing circuits 10, generates periodic sweep gate signals represented by curve C of Fig. 2 occurring, for example, during time intervals ts-ts and ts-ta which are supplied to each of the clamping circuits 32 and 33. Each sweep gate signal is effective to cause, for example, the clamping circuit 32 to unclamp the N-S sweep generator 28 to enable thatgenerator to develop a sweep signal of duration corresponding to the duration of thesweep gate signal. 33 likewise responds to each sweep gate signal to un` clamp E-W sweep generator 29 to permit that generator' to develop a sweep signal in a similar manner. During the intervals intervening the occurrence of the sweep gate signals, for example, the intervals tz-ts and t5 ts of Fig. 2, the clamping circuits 32 and 33 are eiective to disable the sweep generators 28 and 29 and establish and maintain potential reference levels lat the output yterminals of the sweep generators during these intervals to cause the 'scanning beam of the display device 2 2 to strike the center of the display screen 23. In the embodiment represented in Fig. l,v these fixed reference levels are essential in order that the visible portion of each beam scan may start from the same position on the display screen 23.

In order to enable the sweep signals to develop a rotatl example, a sine-wave signal represented by curve D of- Fig. 4. lThis sine-wave signal is effective to control the amplitudes of the individual sweep signals produced by the sweep generator 28 to produce at the output terminals o f generator 28a set of sine-wave modulated sweep signals represented by curve E of Fig. 4. It will be noted thatthe envelope of the amplitude variations of the sweep signals, which envelope is represented by curve D', corresponds to the sine Wave of curve D. The zero The clamping circuit level of curve E represents the reference level which is `precisely maintained by the clamping circuit 32.

In a similar manner, a cosine-Wave -signal is supplied to, for example, the E-W sweep generator 29 to produce at the output terminals thereof a set of cosine-wave modulated sweep signals having amplitude variations similar to those represented by curve E of Fig. 4 except that the peak-amplitude variation of the envelope is shifted by one-quarter of a sine-wave cycle with respect to the peak-amplitude of the envelope of the sweep signals of curve E.

The sets of sinusoidally modulated sweep signals from the sweep generators 28 and 29 are supplied through the corresponding adding circuits 43 and 50 to the corresponding sweep amplifiers 47 and 54 which, in turn, are connected to the corresponding deflection windings 24 and 25 to produce the rotating radial scanning pattern on the display screen 23. Because the sine-cosine signal generator 35 is properly synchronized with the rotation of the directional antenna system 14, 15, each scan of the scanning beam of the display device 22 corresponds to a given angular direction of the antenna system. Each cycle of, for example, the sine-wave signal represented by In order to start the individual beam scans from anl off-center position, it is necessary to supply suitable offcentering signals to the dellection windings 24 and 25. In order that the off-centering position may rotate in accordance with the rotation of the scanning trace, it is necessary that these oif-centeringsignals have sinusoidal variations of the same frequency as the sinusoidal modulation of the sweep signals. As the off-center starting position of each trace is to be located on an opposite` side of the center from the visible portion of each trace, it is necessary that the off-centering signals be of inversepolarity or inverse phase to that of the sinusoidal variations of the sweep signals.

One system for developing and supplying to the dis-.

for example, the sweep generator 28 is also supplied to the phase inverter 38 through a voltage divider 40. The signal produced at the output terminals of the phase inverter 38 is represented by curve F of Fig. 4 and is supplied through the adding resistor 45 to the sweep amplilier 47. As a result of addition of this olf-centering signal to the sine-wave modulated sweep signals supplied by the sweep generator 28, the wave form of the resulting signal at the input terminals of the sweep amplifier 47 is as represented by curve G of Fig. 4. It will be noted that the starting point of each of the sweeps has been shifted with respect to the reference level in accordance with the amplitude of the inverse-phase ol-centering signal as indicated by the lower envelope F of the sweep signals represented by curve G.

The portion of the resulting signal represented by curve G occurring in the time interval ti-ts of Fig. 4 is shown in more detail by curve G of Fig. 2. It will be noted that the amplitude variations of the sweep signals corresponding to the envelopes D and F of Fig. 4 may not be discernible in curve G of Fig. 2 because of the expansion of the time scale thereof and the smallness of the variation. As the zero reference level of curve G of Fig. 2 represents the signal level required for the deflection winding 24 to cause the scanning beam to strike the center of the display screen 23, it will be seen that, as far as deflection winding4 24 is concerned, each of the sweeps now starts from a point with respect to the reference level As shown, the sinewave signal used to control the amplitude variations of,

' startingwposition-to the centerof.the.display:corresponds maestose suche/.that eachtoftthetbeamgscans will-fstartzfrom an ,olicenter positicmron tatsideiopposite @the yisiblefportion--tof eachzsean. -T:o..obtain the. proper star-tingfpositionf fori each scan, ...an nversefphase.cosinewave signal 'ofathe same amplitudelas the inverseephaseYsine-wavesignabof curve F :mustfbe added-tofthescosineewave modulated .sweep signalslfrom'rathe E-W asweep ;generator29 in: the 1san-1e mannerfas was :done for the 1sine-Wave fmodulated .sweep signalsI from the -N -Ssweep generator V28. Y

Thecamount by lwhichseach-:scanstarts-:from an ,offcenter position is indicated by the radius of'thewdashvline circle 641.shownionthevfacefof therdisplay screen 23 -of Eig. 3. f 4 The :amount i of= initial oi-center-ingzmay. be adjusted-byaadjusting ftherarnplitude of: the inversefphaseoffcentering signalsA supplied by;thephase-invertersuand 39, This adjustment isimadeiby, means ot` thetadjustable voltage-1dividersAD-gand ,41. The-famountby which .the starting position :is off-centered should be. such rthat'atl'te time V4requiledifor the :scanning beamato passfromxthe towtthe y tpredeterminedgtime. interval by A`which t ,the sweep signals arefstar/tedgpriortoqthecorresponding radarpulses.y In. orderto..eliminate: the .distortion presentv in the -v initial portion of v`each-sweep, k this time interval vmay be, `for example, v4-,of the ,order `of fourv-times the time constant ofthe;deflection'` windings @which .may ,'be, for example,:of theiorder, offlOOn microseconds. v v y K It is, totbe .11nderstood-..that ther-.term .center ofthe ...displaytscreenisfmot:necessarilytlimitedato meanfthe physicalecenter ofltthe;displayfscreenfz,but rather means the center of the radar scene corresponding to the :location ofrzthe radar antenna. :This distinction is important beeauseitz-is frequent ;practicein present-day .radar systems to Iprovide means Yfforloihcentering the'tentirefradar scene: displayed on :the `displaytdevice inr-forder. to -,aiord atinente` desirablepresentation of :events -toceurring .atr4 the edge of A lthe radar zscene.

From .the..foregoing descriptionftthe, invention in will be r,z ipparent rthatiia radar indicator s sweep deilection l-systemv.,cnstructed in laccordance with f the ;pres'ent innentionirpresents andmprovedesweep,deectionsystem for eliminating displayadistortion rwithoutry need -for ,recourse to complex circuitry. f

While there has been describedffwhattfisfatl'presentconsidered: t0 .be the; preferredfembodiment of thisl invention, it will be obvious .to those-:skilled '.inztheaartfthatvarious changes :andtmodications.,maybennade therein without departing ifrom therf invention, and;it;is, therefore,-t aimed toc covert-.al1 .f suchtf-.changes fandfmodicationslias rfalbe within thefftruesspiriti'andfcscopef o f fthe;invention Y xWhat `istclairnedf is: f Y

. 1.r EA; radar f indicator sweep deilectionzsysterncomprising: fadisplay-deviee includi'nga-.displayl screenvandnne ans for -ascanning i the f display -iscr'eenuwithea beam which is' periodically :unblankedztof-develop onf,the-;display:screen the :display of ftarv-getfechoes `of :'periodic ,radar signals;. circuit means for -figeneratinge :periodic `sweep isignals in herenfilythaving yundesirable characteristics duringthe initial p portions .thereofiand individually starting :a 'predeterminediintervalgpriorztoxthefzcorrespondingradar signal' -f to icontrolisaidfscanningbeam;means for supplying oicenteringsignals` to said display device toena'blexs'ad scanning beam to start fromiannof-center:positionfor eachlscanand:pass:.acrossithezcenteriosaid:.displayzscreen at .the rend .Y of said predetermined '.vinterval; and circuit meansxforlu'nblanking saididisplay 'device-ras said :scanning beam :crosses :over :the ycenter tof lsaid display screen nto enable the device to :display 'the wsubsequent :porti-'on of eaehflsean fwhch ;\is.;coniro`lled -by'bthe :later portions /o'f saidzsweep'esignals.

Z2. SA. radar' indicatorI sweep -de`ection:sys'tem' comprising :v'afdisplaytlevice including adisplaysc'reeniand means foruscanningdthe Idisplay'I screen-With a -beam 'Which-is periodically unblanked 0to 'develop onxthe displayfscr'een thefd-isplayvof target'echoes'-of,periddic^radar signals; a i' 8 pair; 'of sweep-signal generators .fior lgenerating Aperindic sweep signale inherently havingiundesirable. characteristics duringdhe initiallportions1 thereofetol controVlf-saidsqaasng Y.

beam; t ,circuit lmeans iforeindividually 1startingfsaidssixeeep signalsia,predeteruxined-internalf-prior tofithe. conepondging radar signal; means for supplying olf-centeringqig-g nais` toi-said:dispLaytdevieeqto enablesaid scaimingsbeam crosses over fthe, center` of said display ,screen to enable thefdevicetto:displayrthe-tsuhseguent;portionof oachfscan which fis controlled tby\,the -Y Alater portions signals.

. 3. aA, radar .-indicatorffsvreepfldeieetionasystemY comprisingr-*a display deviceiincluding -a-displayisereen and meansA for l radially scanning the Adisplay screen with :fathom whicha-is1v periodically zgunblanke'diito- ,develop t on display screenagplangppsitionvqdisplayof target eehoesnof periodic: radar: signals; :a pairf. ofsweep-signal,generataiz'sl for generating siii-st ftandasecond.` sets'tof gperiodicasweep signals iinherentlyt havingfundesirablecharacteristicsliduring athe @initial-'portions f', thereof l 4zand iindividuaiiyi starting afpredeterxninerl interval priortottheicorrespondingfradar signal toicontrolrsaid scanningrbeam; circuit V`means for varyingtthefamplitudeszof saidsweep signalsiinra sinusnl'del manner, ithetsinusoidal tvariation-offsaidrinsti setY diering infphaserfrcm fthe sinusoidalwarationfofrsaidisecond let by90 toenablet snccessivefradialbeamtseansfto nprzess around theadisplayrscreeniinsaeeircularrnanner; meals forvsupplyingrotf-,eentering .signalsi--tofsaid displayrde'vice toienablersaid-fscanaingfheamzto startfromuan ol'eemter position-1forfieachssoamandtpassfaernss :thementermffsad y displeytscreen atwthe'zend'tofesaidpredetermined nteml;

and,` circuit Emeansiffor iunblankingesaidqdisplay tdeviceiias play f-screen: to; enable the fdevice .to ,display yttlie ssulzsfe-V quent-:portionrofieaehfscan which ,fisomrolled :by ithe 40 laterlport-ionsaofesaid sweepgsignals.

i4. iA radar; indicator sweep deiectionfsysiiemfuimpris-y ing: a-idisplayeviee includingaedisplayfscreen for radially iscanning thefdisplay :screen v-.vvith a beamwhicha is periodically'mnb1ankedztomiewdop iontihe edis# playrscreen agpiaufposition tdisplayroffsar'getfieehs of periodic radarasignals;tapiairfzofsweepfsignlgeneratersfor generatingdrstzand-fsecondisetsmfgpericdic smeep sig'- nals :inherently having` undesirable :characteristics dating the finitial :,'rportions frthereof -fand individually :starting sa r predeterminediintewal priorrtoathe orrpondingzndar signalx to montrol '.scmnng beamnxeircnitameans varying thefarnplitudesonsaidsweepsignalsrinfasinnsdal kmarinier,diiessinusoidal uariationnsaid rstnsetidilering infphaseifromrthe `sinusoidalv aniatioimif aaidfsecoud set byoatofenableiluecessive radialzbeanzscsnsrtozprogmss around the display screen in a circular mannen-.circuit means for zsupplyingfsinusoidal dif-,centering isignals rof inverse'gxphase @to .fthei'sinusoidal '-.amplitude variations nf saidiseiseofisweeprsigials ato; saidf dispiayrdevicee-toaemble sadvseannin'gifbeam to :startifromsanwl-:center i foreachnscan andzpaaseacrossadieacemertofssaidnisplay screen fvatttheffendmf ysaid' predetermined zinterval; .fand circnit'fmeansefomnnblankingrsidfdisplayedevee asiaaid seanningebeam ncrosseseover l@the center :of saidv cdisplay screen-vito 4enable ,thefdevice fto @display the subsequent portionqoeachscanfwhichiistcontrolledybyethe tionsfofasaid sweeptsignals; y

. 5. lA` radanindicator :sweep Atdeilection A`system:eornpnsing: a .display tdevice .including sa tdisplay screen :and

'70 means for. scanninglthejdisplay screen withia beam rwhich x is; periodicallyKunblankedtodevelop on the,;dis p`l.ay. screen the .display/.f ,target echoes ofper`iodic fradarcvsignals; circuit,I means LforA, generatingperiodic sweepfsignals .nher'- ently having undesirablecharacteristics .,duringthe ,initial rportions `thereof and individually starting ,a rpredetermined interval prior to the corresponding radar signal to control said scanning beam; means for supplying otcenterng signals to said display device to enableV said scanning beam to start from an off-center position for each scan and pass across the center of said display screen at the end of said predetermined interval; and an unblanking gate generator for supplying periodic unblanking gate signals for unblanking said display device as said scanning beam crosses over the center of said display screen to enable the device to display the subsequent portion of each scan which is controlled by the later portions of said sweep signals.

6. A radar indicator sweep deection system comprising: a display device including a display screen, flrst and second deection windings, and means for radially scanning the display screen with a beam which is periodically unblanked to develop on the display screen a plan-position display of target echoes of periodic radar signals; first and second sweep-signal generators for generating first and second sets of periodic sweep signals inherently having undesirable characteristics during the initial portions thereof and individually starting a predetermined interval prior to the corresponding radar signal to control said scanning beam; a sine-cosine signal generator for supplying a sine-wave signal to said first sweep-signal generator and a cosine-wave signal to said second sweepsignal generator for varying the amplitudes of the sweep signals of said rst and second sets in a properly related sinusoidal manner to enable successive radial beam scans to progress around the display screen in a circular manner; first and second phase-inverter circuits coupled to said sine-cosine signal generator for respectively developing inverse-phase sine-wave and cosine-wave offcentering signals to enable said scanning beam to start from an off-center position for each scan and pass across the center of said display screen at the end of said predetermined interval; rst adding circuit means coupled to said rst sweep-signal generator and said first phaseinverter circuit for adding said rst set of sweep signals and said inverse-phase sine-wave signal and supplying the combined signal to said rst deflection winding; second adding circuit means coupled to said second sweep-signal generator and said second phase-inverter circuit for adding said second set of sweep signals and said inversephase cosine-wave signal and supplying the combined signal to said second deection winding; and circuit means for unblanking said display device as said scanning beam crosses over the center of said display screen to enable the device to display the subsequent portion of each scan which is controlled by the later portions of said sweep signals.

References Cited in the le of this patent UNITED STATES PATENTS 2,222,943 George Nov. 26, 1940 2,313,966 Poch Mar. 16, 1943 2,386,728 Theisen Oct. 9, 1945 2,395,966 Goldberg Mar. 5, 1946 2,406,970 Smith Sept. 3, 1946 2,540,087 Barchok et al. Feb. 6, 1951 

